Process for preparing silicon tetrachloride from silicon carbide with hydrogen chloride

ABSTRACT

In a process for preparing silicon tetrachloride from silicon carbide and/or silicon carbide containing mixtures with hydrogen chloride the improvement which consists in carrying out the reaction in the presence of cobalt chloride or nickel chloride or a mixture of both at temperatures ranging from 400*C to 1,000*C.

United States Patent 1191 Wiebke et al.

1451 Nov. 18, 1975 PROCESS FOR PREPARING SILICON TETRACHLORIDE FROM SILICON CARBIDE WITH HYDROGEN CHLORIDE Inventors: Giinter Wiebke, Munich; Giinter Stohr, Kempten; Giinter Kratel,

Durach; Johann Kra], Kempten, all. of Germany Elektroschmelzwerk Kempten GmbH, Munich, Germany Filed: Apr. 18, 1974 Appl. No.: 462,072

Assignee:

Foreign Application Priority Data Apr. 19, 1973 Germany 2319995 US. Cl 423/341; 252/441; 260/676 R Int. Cl? C01B 33/08 Field of Search 423/341, 343, 342;

References Cited UNITED STATES PATENTS Arnold 252/441 2,686,819 8/1954 Johnson 260/449 M 2,843,458 7/1958 Beattie 423/343 FOREIGN PATENTS OR APPLICATIONS 728,919 4/1955 United Kingdom 423/341 36-23155 11/1961 Japan 423/342 OTHER PUBLICATIONS Mellor, J. W. A'C omprehensive Treatise On Inorganic and Theoretical Chemistry, Vol. 2, Longmans, Green & Co., (1920), P. 31.

Primary Examiner-Oscar R. Vertiz Assistant ExaminerMichael L. Lewis Attorney, Agent, or Firm-Allison C. Collard [57] ABSTRACT In a process for preparing silicon tetrachloride from silicon carbide and/or silicon carbide containing mixtures with hydrogen chloride the improvement which consists in carrying out the reaction in the presence of cobalt chloride or nickel chloride or a mixture of both at temperatures ranging from 400C to 1,000C.

2 Claims, 1 Drawing Figure PRESSURE (sauce AND a EXCESS RESSURE TOWER VALVE TEMPERATURE REGULATOR containing starting material.

PROCESS F R PREPARiNc 's iLic N TETRACHLORIDE FROM SILICON CARBIDE wmr HYDROGEN CHLORIDE The presentinvention relates to a process for preparing silicon tetrachloride from silicon carbide with hydrogen chloride.

The chlorination of silicon carbide with HCI has been known for a long time and is supposed .to take place at red heat according to the following equation 1 U tained in the production of silicon carbide, such residues lending themselves to the preparation of silicon tetrachloride. (See D.B.P. 1,105,398)" According to the present invention a process now been found for preparing silicon tetrachloride reaction of silicon carbide and/ or silicon carbide-containing mixtures with HCI in the presence of heavy metal chlorides'wherein the reaction is carried, out in the presence of cobalt chloride and/or nickel chloride at temperatures ranging from'400C to 1,000C, and preferably at,

temperatures between 600and" 900C.

Whereas heavy metal compounds, particularly chlorides, are said to be readily carried off, (see H. Schaefer Chemische Transpo'rtreaktionen -Verlag Chemie,

1962) which means that these chlorination catalysts are used up rapidly, this fact has not been observed under the conditions of the process of the invention in the preparation of silicon tetrachloride from silicon carbide with hydrogen chloride, and the silicon carbide used is almost completely converted in the reaction.

The amount of cobalt chloride and/or nickel chloride which catalyzes the reaction of silicon carbide with HCI, is 0.1 30 percent by weight, preferably 1 10 percent by weight calculated on the silicon carbide- ,The catalyst can be added to the silicon carbide in solid form, e.g., as powder. As a rule, the metal compound is added to the silicon carbide from a solution. The solvent used for this purpose is water or diluted hydrochloric acid.

The catalyst can also be introduced into the reaction chamber by impregnating an inert carrier, suchas SiO and active carbon, in mixtures with silicon carbide.

The silicon carbide used in the preparation of the silicon tetrachloride is mostly conventionally prepared, technical silicon Carbide, but mixtures of materials containing silicon carbide, for instance ceramic materials having a content of silicon carbide, may also be used.

The silicon carbide can be chlorinated in granulated form in a fixed bed reactor, or preferably in powder form or in the form of very small grains in a fluidized bed reactor, in a continuous operation. Before the reaction takes place, the filling is dried by means of an inert gas, e.g. by nitrogen, and heated up to reaction temperature. It is advantageous to dry the HCl, too, be-

fore application.

To heat up the reactorto the reaction temperature, suitable-fuels as for example. silicon metal, ferrosilicon, silizides andsimilar compounds may be used. The chlorination is an exothermal reaction and may, therefore, be carried out autothermally. If, nevertheless, heat losses occur, they can be compensated addition 0 of thabove named fuels.

' "In the "accompanying drawing -an arrangement for carrying out the invention is schematically illustrated. The device comprises: a bottle of hydrogen chloride, designated by 1, a bottle 2 containing nitrogen, a manometer 3 serving at the same time as excess pressure valve, when pressure accumulates in the reactor. A drying tower 4 and a rotameter 5 are likewise provided. A main pipe line 20 connects bottle 1 to drying tower 4 with branch lines leading to the main line from bottle 2 and manometer 3. Appropriate connecting lines 22 and 24 are also provided for leading from drying tower 4 to rotameter 5 and from there to a reactor 6, respectively. In the reactor tube the conversion of silicon carbide into silicon tetrachloride takesplace. The tube consists of quartz or aluminum oxide-containing material which 'The temperatureis maintained at a constant level by a regulator7' connected totu be 6 over an ampere-meter Aq'ln the reaction zone and at the entrance of the same, the temperature is checked by two thermocouples, 8 and9 respectively. A gas permeable graphite'cushion ll' arranged within the tube 6 serves as a support for the granulated silicon carbide 10 to be reacted with HCI gas, dried by nitrogen; the HCI enters the reactor at an inlet 14 in the bottom closure 15. The gaseous reaction product escapes at the top through line '16 and is collected in a trap. 12 cooled by acetone and CO the following, the process of the invention will be mdre fully described in a number of examples which are givenby way of illustration only, and not by way of limitation.

EXAMPLE 1 HCI Reactor HCI Conversion of Si passage Temp. conversion into SiCl,

in 4 hrs.

50 l/h 700C 60.7% 95% by weight EXAMPLE 2 45 g SiC of a grain size 1 3 mm are mixed with 3.5

\ g granulated carbon of the same grain size, which were sult.

Instead of Co' chloride 6 H 0, 5 g nickel" chloride 6H O are placed into the fixed bed reactor and the chlorination performed as in example 1.

The following table shows operation data and result.

HCl Reactor HCl conversion of Si passage temp. conversion into SiCl,

in 4 hrs.

50 l/h 700C 48% 90% by weight EXAMPLE 4 43 g SiC, grain size 180-200um are impregnated with 7 g Co 'chloride 6 H O from an aqueous solution; after drying for an hour in an N current of 50 1/h and heating to a temperature of 700C, the chlorination is carried out as in example 1. However, instead of carrying out the reaction in a fixed bed reactor a fluidized be reactor is used in one case, and a reactor with a stirrer in another case.

The following table shows reactional data and results.

HCI Reactor HCI Conversion of Si passage temp. conversion into SiCl in 4 hrs.

Fluidizcd bed reactor 700C 80% 99.5% by weight -continued HCl Reactor HCI Conversion of Si passage temp. conversion into SiCL in 4 hrs.

50 l/h Reactor with stirrer 700C 92% 99.5% by weight EXAMPLE 5 To 50 g SiC ofa grain size 1 3mm, 2.7 g Co" chloride 6H O and 2.7 g nickel 'chloride 6 H O are added from an aqueous (50 ml) solution. The mixture is reacted with HCl in the device described in the drawing and in the manner indicated in example 1, after having been dried with an N current for one hour, (heating temperature 700C).

Operational data and result are shown in table below.

HCI Reactor HCl Conversion of Si passage temp. conversion Into SiCl in 4 hrs.

50 l/h 700C 64% 99.6% by weight It will be obvious to those skilled in the art that other changes and variations can be made in carrying out the present invention without departing from the spirit and scope thereof as defined in the appended claims.

What is claimed is:

1. In a process of preparing silicon tetrachloride from silicon carbide and silicon carbide-containing mixtures by reacting with hydrogen chloride the improvement, which consists in carrying out the reaction in the presence of a member of the group consisting of cobalt chloride, nickel chloride and a mixture of both, at temperatures ranging from 400C to 1000C.

2. The process as claimed in claim 1, wherein the reactiog is carried out at a temperature between 600 and 900 

1. IN A PROCESS OF PREPARING SILICON TETRACHLORIDE FROM SILICON CARBIDE AND SILICON CARBIDE-CONTAINING MIXTURES BY REACTING WITH HYDROGEN CHLORIDE THE IMPROVEMENT, WHICH CONSISTS IN CARRYING OUT THE REACTION IN THE PRESENCE OF A MEMBER OF THE GROUP CONSISTING OF COBALT CHLORIDE, NICKEL CHLORIDE AND A MIXTURE OF BOTH, AT TEMPERATURES RANGING FROM 400*C TO 1000*C.
 2. The process as claimed in claim 1, wherein the reaction is carried out at a temperature between 600* and 900*C. 